Foraminifera and Radiolaria
Foraminifera and radiolaria are amoeboid protists whose mineralized shells are among the most important microfossils for dating and paleoceanography.
Definition
Foraminifera are single-celled protists that build chambered tests of calcium carbonate or agglutinated grains, while radiolaria are protists with ornate silica skeletons; both are major marine microfossils.
Scope
This topic covers the biology and shells of foraminifera, with their calcareous or agglutinated tests, and radiolaria, with their siliceous skeletons, including both planktonic and benthic forms and their applications in biostratigraphy and paleoenvironmental reconstruction.
Core questions
- How do planktonic and benthic foraminifera differ in ecology and use?
- What makes foraminiferal tests good geochemical archives?
- How are radiolaria used to date and interpret deep-sea sediments?
- How do test chemistry and morphology record environment?
Key concepts
- Calcareous and agglutinated tests
- Planktonic versus benthic foraminifera
- Siliceous radiolarian skeletons
- Oxygen and carbon isotope proxies
Key theories
- Foraminiferal oxygen-isotope paleothermometry
- Oxygen-isotope ratios in foraminiferal calcite record past temperature and global ice volume, underpinning the standard record of Cenozoic climate and ice ages.
- Radiolarian biostratigraphy
- Rapidly evolving radiolarian assemblages provide zonation of siliceous deep-sea sediments where carbonate is dissolved.
Clinical relevance
Foraminifera are workhorses of petroleum biostratigraphy and the primary archive for reconstructing past ocean temperature, salinity, and ice volume, while radiolaria date silica-rich sediments and track ocean productivity.
History
Foraminifera were studied from the nineteenth century and became central to oil exploration and, after Cesare Emiliani's isotope work in the 1950s, to paleoclimatology. Radiolaria provided some of the first detailed zonations of deep-sea cores.
Debates
- Diagenetic alteration of test geochemistry
- How far burial and recrystallization bias isotope and trace-element signals in foraminiferal tests is an ongoing methodological concern.
Key figures
- Cesare Emiliani
- Alfred R. Loeblich
- Helen Tappan
Related topics
Seminal works
- haq1998
- armstrong2005
Frequently asked questions
- Are foraminifera animals?
- No, foraminifera are single-celled protists, not animals, though they build complex shells that look like tiny snail or chambered structures.
- How do forams tell us about past climate?
- The chemistry of their calcite shells, especially oxygen isotopes, records the temperature and ice volume of the oceans when they lived.